PSAT Math : Operations with Fractions

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #13 : Operations With Fractions

Solve \frac{3}{7}+\frac{5}{8}-\frac{1}{2}\(\displaystyle \frac{3}{7}+\frac{5}{8}-\frac{1}{2}\).

Possible Answers:

\frac{33}{56}\(\displaystyle \frac{33}{56}\)

\frac{31}{56}\(\displaystyle \frac{31}{56}\)

\frac{5}{7}\(\displaystyle \frac{5}{7}\)

\frac{7}{8}\(\displaystyle \frac{7}{8}\)

Correct answer:

\frac{31}{56}\(\displaystyle \frac{31}{56}\)

Explanation:

Finding the common denominator yields \frac{24}{56}+\frac{35}{56}-\frac{28}{56}\(\displaystyle \frac{24}{56}+\frac{35}{56}-\frac{28}{56}\). We can then evaluate leaving \frac{31}{56}\(\displaystyle \frac{31}{56}\).

Example Question #31 : Operations With Fractions

What is the solution, reduced to its simplest form, for x = \frac{7}{9}+\frac{3}{5}+\frac{2}{15}+\frac{7}{45}}\(\displaystyle x = \frac{7}{9}+\frac{3}{5}+\frac{2}{15}+\frac{7}{45}}\) ?

Possible Answers:

x =2\(\displaystyle x =2\)

x = \frac{7}{15}\(\displaystyle x = \frac{7}{15}\)

x = \frac{115}{45}\(\displaystyle x = \frac{115}{45}\)

x = \frac{75}{45}\(\displaystyle x = \frac{75}{45}\)

x = \frac{5}{3}\(\displaystyle x = \frac{5}{3}\)

Correct answer:

x = \frac{5}{3}\(\displaystyle x = \frac{5}{3}\)

Explanation:

x=\frac{7}{9}+\frac{3}{5}+\frac{2}{15}+\frac{7}{45}=\frac{35}{45}+\frac{27}{45}+\frac{6}{45}+\frac{7}{45}=\frac{75}{45}=\frac{5}{3}\(\displaystyle x=\frac{7}{9}+\frac{3}{5}+\frac{2}{15}+\frac{7}{45}=\frac{35}{45}+\frac{27}{45}+\frac{6}{45}+\frac{7}{45}=\frac{75}{45}=\frac{5}{3}\)

Example Question #131 : Fractions

What is the sum of \(\displaystyle \small \frac{4}{5}\) and \(\displaystyle \small 2 \frac{5}{6}\)?

Possible Answers:

\(\displaystyle \small \frac{109}{30}\)

\(\displaystyle \small \frac{30}{109}\)

\(\displaystyle \small \frac{79}{30}\)

\(\displaystyle \small \frac{49}{109}\)

\(\displaystyle \small \frac{49}{12}\)

Correct answer:

\(\displaystyle \small \frac{109}{30}\)

Explanation:

We can begin by eliminating the obviously wrong answers. We know that the sum of the two fractions will be more than 1, so the answer choices \(\displaystyle \tiny \tiny \frac{49}{109}\) and \(\displaystyle \small \frac{30}{109}\) are out. Now, let's add the two fractions:

Begin by converting \(\displaystyle \small 2 \frac{5}{6}\) to \(\displaystyle \tiny \frac{17}{6}\).

Now find the common denominator of \(\displaystyle \small \frac{4}{5}\) and \(\displaystyle \tiny \frac{17}{6}\). The least common multiple of 5 and 6 is 30, so 30 is the common denominator. Now alter both fractions so that they use the common denominator:

\(\displaystyle \tiny \small \frac{4}{5}= \frac{4*6}{5*6}=\frac{24}{30}\)

 \(\displaystyle \tiny \small \frac{17}{6}=\frac{17*5}{6*5}=\frac{85}{30}\)

Now we can easily add the two fractions together:

\(\displaystyle \small \frac{24}{30}+\frac{85}{30}=\frac{109}{30}\)

The answer is \(\displaystyle \small \frac{109}{30}\).

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